The long-term objectives of this proposal are 1) to understand the mechanism by which tissue interactions regulate morphogenesis, histogenesis and biochemical differentiation (keratinization) during the development of the vertebrate integument, and (2) to understand how the epidermal basal cell populations (stem cells) of the various skin appendages become committed to their tissue-specific forms of histogenesis and keratin gene expression. The specific aims are 1) to produce polyclonal and monoclonal antibodies which specifically recognize (in tissues and on immunoblots) the individual alpha and beta keratin polypeptides of the avian integument separated by 2-dimensional gel electrophoresis, 2) to define the sequence in which keratins are expressed (by 2-d gel electrophoresis, and indirect immunofluorescence) during the development of the scutate scales, reticulate scales, feathers and general body skin from normal chicken embryos and embryos which have genetically based skin disorders, 3) to correlate the appearance of individual keratin polypeptides with the fine structural events occurring during epidermal histogenesis of the various skin appendages, 4) to determine if dermal tissues induce the same sequences of fine structural events and the same keratins when they are recombined with foreign epithelia, such as the chorionic epithelium or scaleless epidermis, 5) to determine if presumptive scutate scale dermis can acquire the ability to induce a Beta Stratum in the absence of scutate scale epidermis, and, finally, 6) to determine when the embryonic scutate scale epidermis no longer requires scutate scale dermis in order to elaborate a Beta Stratum. These studies are of particular importance to the understanding and control of the numerous skin disorders, affecting the human population.